Gravel packing is used as a means of controlling sand production and to consolidate and prevent the movement of failed sandstone and/or increase the compressive strength of the formation sand. It can also serve as a filter to help assure that formation fines and formation sand do not migrate with the produced fluids into the wellbore. In a typical gravel pack completion, gravel is mixed with a carrier fluid and is pumped in a slurry mixture through a conduit, often drill pipe or coiled tubing, into the wellbore. The carrier fluid in the slurry is returned to the surface through a separate tubular or an annulus area, leaving the gravel deposited in the formation, perforation tunnels and wellbore where it forms a gravel pack.
High friction pressure is a known problem in gravel packing used in sand control and for supporting the matrix surrounding the wellbore, especially for high rate water packs in long open-hole intervals, such as those longer than 3000 ft. (915 m). High friction pressure is undesirable because it can result in high pressures in open hole sections that can exceed the fracturing pressure of the formation. Unintended fracturing during a gravel pack treatment leads to incomplete packing and loss of gravel to the formation, ultimately impairing productivity. If no friction reducing additive is used, when pumping through a 8.5 inch (21.6 cm) casing with 5.5 inch (14 cm) production tubing, for example, the pressure can rise up to that of water, namely up to 110 psi/1000 ft in the tubing (18 kPa/m of pipe) or up to 80 psi/1000 ft (14.5 kPa/m of casing) in the annulus when pumped at 20 barrels per minute (0.053 m3/s). For wells at high depths, such as 20,000 ft. (6090 m), or 30,000 ft. (9144 m), excessive friction pressure can alter the well design in terms of limiting the drilled length of an horizontal zone, or in other cases being the difference between being able to effectively pumping a gravel packing or not when the pumping power at surface is limited.
Known methods to reduce friction pressure include the use of polymer-based gravel packing fluids and friction reducers, chemical additives known to reduce the friction pressure of flowing fluids. These polymers and friction reducing agents are added at the surface with the gravel packing fluids. The conventional polymeric friction reducing agents can degrade when exposed to high shear zones in the pipes or downhole tools due to shear induced degradation during the treatment, however, allowing pressures to increase over time.
Additionally, polymer materials that are combined with the gravel packing fluids at the surface to reduce friction can impair the flow through the gravel pack after the gravel packing operation is completed. Fluids from the reservoir may also reduce the effectiveness of the friction reducers added at the surface. The majority of the friction occurs between the washpipe and the screen in the return flow of fluid during the gravel packing treatment.
New methods are therefore needed for reducing friction in such types of treatments to overcome these and other obstacles.